The invention comprises a steering shaft for motor vehicles having an inner and an outer shaft part. Each shaft part has a polygonal cross section. The shaft parts are telescopically engaged and are positively connected to one another by barrel-shaped rolls that are effective as rolling elements for the transmission of a torque. Each running path of the rolls is fashioned between vertices on the outer sides of the inner shaft part and the inner sides of the outer shaft part. In one aspect of the invention, the running paths are fashioned as troughs of a concavity approximating to the convexity of the rolls.
Because of the adaptation of the cross-sectional shape of the running paths to the external generating curves of the rolls, a heightened surface pressure does not occur for either of the loading modes to which a steering shaft is subjected in service, whether in the face edge region of the rolls in the case of torsional loading, or over the longitudinal extent of the rolls when the two shaft parts telescope relative to one another. Thus, the useful life of the steering shaft is extended.
In yet another aspect of the invention, the running paths are at least surface-hardened or strengthened in any suitable manner. In this way there is a marked extension of the time span within which the working of the steering shaft remains backlash-free and easy to use, even under extremely high and frequent loading.
In another aspect of the invention, the rolls are guided in a cage.
In yet another aspect of the invention, the steering shaft comprises spring elements that are arranged between at least two opposite running paths. The spring elements are directly or indirectly braced under spring force against the respective running paths. The pressure applied to the inner shaft part presses the rolls guided on the other running paths against the outer shaft part, so that any play that may be present as a result of tolerance is compensated. Hence, in this way, torque transmission is effectively distributed.
The spring elements are preferably fashioned as leaf springs and are able to abut a pad. The pad abuts the inner shaft part and can be formed of any suitable material, e.g., plastic. Through a determinable friction coefficient of the pad, the ease of use brought about by the rolls is maintained when there is an axial displacement between the inner and the outer shaft part.
In one aspect of the invention, the spring elements are situated in chambers of the cage, specifically between two rolls. A plurality of chambers can be distributed over the length of the cage. In one aspect of the invention, one or optionally a plurality of spring elements are arranged in each chamber.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments thereof, as illustrated in the accompanying drawings.